sufB

sufB (PBANKA_API00120) is an apicoplast-genome-encoded component of the plastid SUF pathway for [Fe-S] cluster biogenesis in malaria parasites (PMID:12594924, PMID:28695709). In Plasmodium falciparum, the sufB product physically interacts with the nuclear-encoded, apicoplast-imported ATPase SufC, an interaction demonstrated both between recombinant proteins and by co-elution of native SufB from parasite lysate, with an internal region of SufB sufficient for binding (PMID:12594924, PMID:21722645). SufB additionally associates with SufD, and the three proteins assemble into a SufBC2D complex that functions as a scaffold capable of assembling [4Fe-4S] clusters in vitro, as shown by reconstituted cluster-assembly assays and in vivo cross-linking (PMID:28695709). Distinct from its bacterial counterpart, P. falciparum SufB itself exhibits ATPase activity, indicating functional specialization of the plastid Suf machinery (PMID:21722645). Beyond its role as a scaffold subunit within this apicoplast complex, no further mechanistic detail specific to PBANKA_API00120 has been characterized in the available corpus.

1. 2003 Medium

   Establishing whether the apicoplast-encoded sufB protein has a functional partner addressed whether malaria parasites operate a plastid SUF pathway that bridges genomes; the finding showed sufB physically engages a nuclear-encoded partner.

   Evidence Physical interaction assay between apicoplast-encoded SufB and nuclear-encoded SufC (ycf16) in Plasmodium falciparum

   PMID:12594924

   Open questions at the time

   • Single interaction experiment reported in a review-style paper without stoichiometry or interface mapping
   • No functional consequence of the interaction demonstrated
   • No cluster-assembly activity tested
2. 2011 Medium

   It was unknown whether the SufB-SufC interaction occurred in a parasite context and whether SufB carried enzymatic activity; reciprocal pulldowns plus a biochemical assay confirmed the interaction and revealed that Plasmodium SufB, unlike bacterial SufB, has ATPase activity.

   Evidence In vitro interaction with recombinant proteins, affinity co-elution of SufB from P. falciparum lysate, and ATPase activity assay of recombinant PfSufB

   PMID:21722645

   Open questions at the time

   • The interaction-sufficient internal region of SufB was not resolved structurally
   • Physiological relevance of SufB ATPase activity to cluster assembly not established
   • Single-lab characterization
3. 2016 Low

   Whether SufB pairs with additional scaffold factors was probed in a second species; modeling and localization data placed SufB alongside SufA in apicoplast Fe-S pre-assembly, though the direct evidence concerned SufA rather than SufB itself.

   Evidence Computational modeling of the SufA-SufB interface and fluorescence-microscopy apicoplast localization of SufA in Plasmodium vivax

   PMID:27033210

   Open questions at the time

   • Interface prediction is computational with no experimental validation of the P. vivax SufA-SufB contact
   • Localization data are for SufA, not sufB itself
   • No direct demonstration of sufB scaffold function in P. vivax
4. 2017 High

   It was unresolved whether SufB-containing assemblies could actually build metal clusters; reconstitution showed SufB forms a SufBC2D complex that acts as a functional scaffold assembling [4Fe-4S] clusters in vitro.

   Evidence In vitro protein interaction assays, in vivo chemical cross-linking, and reconstituted [4Fe-4S] cluster assembly assay in Plasmodium falciparum

   PMID:28695709

   Open questions at the time

   • Cluster-transfer to downstream apoprotein acceptors not demonstrated
   • Stoichiometry and structural architecture of SufBC2D not resolved
   • In vivo requirement of sufB for parasite viability not tested via genetics in this study

• Whether PBANKA_API00120 (the Plasmodium berghei sufB ortholog itself) is essential and how the SufBC2D scaffold transfers assembled [4Fe-4S] clusters to downstream apicoplast acceptors remains unestablished in the available corpus.
• No direct functional or genetic data on the P. berghei gene itself; all mechanistic evidence derives from P. falciparum and P. vivax orthologs
• Downstream cluster-recipient proteins not identified
• Structural model of the assembled complex absent